a) Field of the Invention
The invention is directed to an optical arrangement for stereoscopic viewing of objects which is outfitted with an imaging system and with at least one lens group with a fixed focal length which is arranged between the imaging system and a viewed object for changing the imaging scale.
b) Description of Relevant Principles and Art
Optical arrangements used for imaging objects have the possibility of focusing on these objects and adjusting the imaging focus. The apparatus provided for this purpose can be categorized according to three basic principles:
According to a first principle, the object and the imaging system are moved relative to one another for focusing; that is, either the imaging system is displaced in the direction of the object or, conversely, the object is displaced in the direction of the imaging system as, for example, in microscopes in which the objective is displaced based on the principle of objective focusing or the object support, or slide, with the object is moved based on the principle of table focusing.
In contrast, in a second principle, the focus adjustment is carried out with a constant distance between the object and imaging system in that an optical component of the imaging system is displaced axially relative to other components of the imaging system and the imaging system is accordingly focused on the object. Binoculars, photographic objectives and video cameras operate on this principle.
In optical arrangements based on a third principle, the transmission length is changed by an optical auxiliary system which is arranged between the object to be imaged and the imaging plane of the imaging system. In this way, the object position can be adapted to without intervention in the internal construction of the imaging system and without changing the position of the imaging system relative to the object. The invention described in the following must also be classed in this category.
Optical arrangements for stereoscopic imaging of objects in which, based on the third principle mentioned above, a supplementary optical system in the form of a lens group serving to change the imaging scale is positioned between a fixed imaging system and the object are known in the art.
Depending upon the particular application, such supplementary systems have a positive or a negative focal length. Greenough type microscopes in particular are outfitted with supplementary systems such as these. For example, the “DV 4” and “Stemi 2000” stereomicroscopes by Carl Zeiss Jena GmbH are known in which a fixed magnification factor is achieved with the supplementary system.
The use of supplementary systems is also known for telescope type stereomicroscopes, for example, the “TECHNIVAL” and “CITOVAL” stereomicroscopes described in Beyer/Riesenberg, “Handbook of Microscopy”, Verlag Technik Berlin, third edition, 1998, 348ff. In this case, also, the transmission length is defined by the choice of magnification range and a change is possible only by changing the supplementary system or exchanging the base objective.
This is disadvantageous for applications in which a variable distance to the object to be viewed must be spanned by a stationary optical arrangement, which is required, for example, in restoration work. In this case, an upright, non-reversed image is needed, which can only be achieved with an imaging scale greater than “zero”.
As is well known, either a real intermediate image or a virtual intermediate image is generated in the object plane of the stereomicroscope for this purpose. The invention described in the following is directed to the generation of virtual intermediate images.